One of the most stressful and aggravating problems encountered in the sedentary work force involves the question of proper body support in a seated position. This is particularly true for people suffering back problems since an extremely large percentage of the civilized world's population experience such problem. The present invention relates to a neutral posture chair, and in particular to a neutral posture surgical chair for microsurgeons which reduces or eliminates fatigue experienced by the surgeon due to body posture during microsurgical procedures while the surgeon performs microscopic operations while seated.
Microsurgery is a practice of operative surgery utilizing magnification. The surgeon sits to increase his stability, steadiness, and precision. It is not uncommon for a surgeon to be seated for an extremely long period of time, up to as many as twelve hours fo complicated surgeries such as might be experienced in surgical replantation procedures and the like. Microsurgery presents many special problems regarding visual information, fine manipulation, and tremor control. Among the factors which affect tremor are the body posture, point of limb support, direction of movement, design fo rotatability, and strenous exertion. During extended seated operations, muscular fatigue occurs in the low back, the mid back, the upper back, the shoulders, the neck, the feet, the lower legs, the upper legs, and in the buttocks.
Ergonomics, defined as "the study as man-machine interface", has promoted research in the area o environmental conditions and their effect on work. Many of the findings of the Erogonomics study have been implemented in the industry, particularly in Europe. Ergonomics findings have been applied to the aerospace program in the United States through extensive studies at the National Aeronautics and Space Administration Space Center in Houston on the influence of zero-g and acceleration on the human factors of spacecraft design. However, Ergonomics has all but been ignored in a surgical context because of the intense interest in the practical details of operative procedures. However, the newness and the technical problems of microsurgery have provided a special opportunity to develop the application of Ergonomics to surgery.
In a study by A. C. Mandal, "The Seated Man in 1981", it was indicated that almost half of the industrialized world is thought to be suffering from some form of back complaints. Although industry has made many advances toward eliminating back injury through improved mechanical material handling device systems, cost every year for sick pay, medical treatment, hospitalization, rehabilitation, placement of the physically restricted worker, and disablement compensation and pensions consume enormous sums of money and are exponentially increasing. As industry makes advances in technology, computerization, and material handling, there are concomitant increases in sedentary tasks as the amount of seated time increases. Every day people sit for many hours in many supposedly comfortable and biomechanically designed chairs, such as office chairs, lounge chairs, automobile or airline seats. Notwithstanding the special seat designs, the most common complaints of people with back pain is the inability to sit in comfort, with accompanying difficulty in straightening the back on rising.
Therefore, it is the purpose of this invention to provide and improve neutral posture chair structure which overcomes the disadvantages of the prior art systems and the fundamental misconceptions as to the correct sitting posture. The present invention provides a chair structure which is less fatiguing and more comfortable to sit in based on the neutral body posture position. The conventional correct sitting posture was generally thought to be that the body should be upright with the back straight, where the upper leg forms a 90 degree angle with the trunk; the lower leg forms a 90 degree angle to the upper leg, and the upper arms are hanging vertically at a person's side with the lower arm 90 degrees to the upper arm. However, studies of the type mentioned hereinabove, including those taken in weightlessness and under water conditions have found that the body assumes a neutral posture position where the upper leg forms of an angle with respect to the trunk of approximately 127 degrees and the lower leg forms approximately the same angle with respect to the upper leg. This angle varies slightly due to the physical structure of particular individuals and may vary somewhere between 105 and 135 degrees. It has also been found that a more upright posture for performing sedentary tasks is better for breathing and swelling of the ankles is reduced, legs are able to move more freely, and rising from the seat is easier because the posture is a compromise between standing and sitting. Further studies have also found that a good chair structure should permit changing of the posture which facilitates blood flow and venous return which will help prevent fatigue. An important component of a chair is a well designed back rest which permits support of the lumbar spine yet does not interfere with desired movement of the shoulders and the arms. Levels of disk pressure and electromyography fall when the back of a seated subject is supported. When a chair includes foot controls, back rests provide resistance to force utililize in operating these controls. In particular, foot controls for microsurgery supports allow manipulation of the various controls necessary for the microsurgery thereby eliminating the need of the gloved hands of the surgeon to touch controls allowing them to remain sterile for the duration of the operation.
Electromyogram is the electrical signal associated with the contraction of a muscle. When the body assumes a more neutral posture position, the electromyogram signals decrease indicating a reduction in muscle contraction which results in less fatigue and increases the ability of the seated person to remain in the optimum position for longer periods of time.
Microsurgical chairs which form the present state of the art generally consist of a base structure having three, four or five legs, a flat seat, and some type of adjustable back rest, although a number of microsurgical stool designs eliminate the back rest because microsurgeons tend to sit on the front edge of the seat tilted over the operating table with the abdomen supported so as to be in a leaning over position with the lower arms supported by the operating table, the patient, or mechanical supports specifically designed for that purpose. In studies, it has been found that the surgeon's posture while performing microsurgery tends to not conform to the structural features of the chair, but rather the surgeon assumes more of a sit-stand posture and sits on the front edge of the seat pan primarily because the diameter of the seat pan allows only minor trunk/thigh angle variation. In this position, the surgeon very seldom utilizes a back rest if it is provided and the abdomen is placed against the table or the table extensions. The surgeon places the elbows on the table, table extensions, or does not utilize support in this area. The wrists are usually placed on the patient or on wrist rests. It has been found that the surgeon utilizes all available foot room area and very frequently changes the positions of the lower legs and feet during the course of an operation. The seated posture recommended by Mandal and the NASA studies, among others, appears to closely approximate the seated position of the microsurgeons observed.
In order to overcome the shortcomings of the prior art surgical chairs, as well as chairs in general, the present invention was developed. The present invention is an adjustable chair adapted to support a user in a neutral body posture position, that is the position that the body assumes during weightlessness wherein the muscle, tendon and ligament systems acting on the joints are in total balance and the trunk of the body forms an angle of approximately 127 degrees with respect to the upper legs and the upper legs form a similar angle with respect to the lower legs. With this invention, the user is supported in a posture normally assumed by the body in weightlessness while acting in a normal lg gravity environment. This enables microsurgeons and others in similar sedentary environments to maintain the most natural position the body can assume thereby eliminating the major causes of stress and strain which result from other body positions.
Various factors were considered in the development of the invention, including stability and mobility of the chair. The controls frequently utilized to adjust the height and the tilt of the seat pan as well as the horizontal adjustment of the backrest are foot operated allowing the gloved hands of the surgeon to remain sterile during the operation. The backrest is adjustable both vertically and horizontally and the seat pan height is adjustable to accommodate the various anthropometric differences in the users of the chair and the variable postures they may want to attain. The seat pan tilt is also adjustable so that a trunk/thigh angle of between 90 and 140 degrees is obtainable thereby permitting a change of posture to promote blood distribution and allow for individual variability for the best trunk/thigh angle. The seat pan design also provides a counter ejection force by incorporating a saddle design and further provides additional surface area and support for the thighs by an extension of the seat pan forming leg troughs. Various other features common to microsurgical chairs are included in the present design, including foot rests, conductive casters, sterile construction and material, and so forth.
More specifically, the neutral posture surgical chair of the present invention employs a molded saddle type seat having leg troughs which extend downwardly to support the thighs of the user and a seat pan supporting the pelvic area which includes a central elevated pommel to support the user in the seat when it is tilted. The seat portion is adjustably positioned on a vertical support structure and includes hydraulically operated foot controls which enable the seat to be raised and lowered and tilted to various angles between 90 and 140 degrees with respect to the vertical, preferably at an angle of approximately 127 degrees. The seat structure includes a hydraulically adjustable back support as well as foot rests which are supported on the base of the chair and which are adjustable between an angle of 0 to 15 degrees to accommodate the feet of the user.
Among the objects of the present invention are the provision of a chair adapted to support a user in the neutral body posture position a body would assume in a weightlessness condition, the provision of a chair adapted to position the body of a user in the neutral body position to enable the user to sit in the chair for extensive periods of time in a most comfortable manner without experiencing stress and fatigue normally associated with sedentary positions. A further object of the present invention is to provide a neutral body posture chair specifically designed for use in microsurgery to enable the surgeon to perform tedious operations without attendant inefficiency caused by stress and fatigue.